2000 Jimmy 4.3 vortec Hesitation

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troublecode - 02 Jul 2007 19:42 GMT

Problem: Hesitation/Lack of Power/Slow (Stumbling) RPM Increase on
Acceleration from Idle or Cruise at Moderate Speeds. Occurs 70 - 80%
every time. Can be Duplicated in Neutral in Garage. Condition occurs
with Hot or Cold Engine. Vehicle always starts and idles normally, as
if no problem exists

Parts Repaced in last 2 months:
Fuel Pump & Sock
Fuel Filter
A/C Spark Plugs
Dist. Cap & Rotor
Spark Plug Wires
Ignition Module (Coil Driver)
MAP Sensor
TPS Sensor

Injectors Chemically Cleaned 3X
Fuel Pressure: 61 PSI (Pump Running)
58 PSI (Pump Off)
52 PSI (Engine Running at Idle)
57 PSI (Engine under Acceleration)
Cam Retard at -7 degrees, CRK Learn - Successful
No DTC's Set - No SES Light On
All Grounds Checked and Seem to be Intact.

Scanner will indicate an indiscriminate random misfire, at times, on
various cylinders, when cracking open throttle while parked, in
neutral, when hesitation problem occurs.

Scanner indicates all other sensor readings normal and functioning
correctly.

I am running out of hair to pull out, (and ideas), hoping for comments
or suggestions.

thanks

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boxing@sasktel.net - 03 Jul 2007 05:22 GMT

my 97 suburban does the same thing but only when it is hot. i am
starting to think of installing a cooler thermostat. let me know when
you figure out what is wrong with your jimmy. The only thing I don't
see on your list is replacing the exhaust system. I did that on mine
and its no better. Maybe a muffler shop can test to see if the exhaust
system is plugged.
I should have had mine tested before spending all that money.

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boxing@sasktel.net - 03 Jul 2007 05:50 GMT

i found this post on another board
Then I moved on to the Mass Airflow Sensor. I removed the airfilter
unit, disassembled the Mass Airflow Sensor unit that is right behind
the airfilter. It's a square metal block shape sandwiched in the
flexible rubber air ducting. It also has an electrical connection to
it. Just disconnect the electrical connector, pull the 4 torx screws
out, carefully pull off the metal cover and then the MAS will pull
right off. Be really careful with the MAS, it's expensive and
delicate. I sprayed the daylights out of small sensor wires using CRC
MAS Cleaner ($8 at PepBoys) but still two of the three wires still
looked black in the center, thicker area of the wire. Almost a charred
look ... I thought I was off to the parts store again. But I went
ahead and got a pencil eraser (I read this in another post ... I
didn't just think this up on my own) and VERY, VERY carefully rubbed
the wires to get the gunk off. Be very patient and gentle! It did
clean them up to where they looked like silver wires again. Then
sprayed them again with the rest of the can of cleaner. Let everything
dry about 20 mins and reassembled. My van is now running like it did
years ago ... more power, better sounding and the SES Light went off
on it's own! I have to believe that cleaning the Mass Airflow Sensor
did the trick. Very, very easy to do.
http://www.chevroletforum.com/m_8072/tm.htm

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troublecode - 03 Jul 2007 15:20 GMT

On Jul 2, 11:50 pm, box...@sasktel.net wrote:

> i found this post on another board
> Then I moved on to the Mass Airflow Sensor. I removed the airfilter
[quoted text clipped - 17 lines]
> on it's own! I have to believe that cleaning the Mass Airflow Sensor
> did the trick. Very, very easy to do.http://www.chevroletforum.com/m_8072/tm.htm

I do hate to admit this, but cleaning the MAF Sensor did solve my
problem. My SES Light was not on and I had no DTC's, (for MAF or
anything else), and my scanner displayed the MAF signal responding
normally or as expected

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